Theophylline, a phosphodiesterase inhibitor, is known to inhibit lymphocytes transformation. Lymphocytes from patients with open-angle glaucoma are more sensitive to Theophylline than normal lymphocytes. Therefore, phosphodiesterase levels are being measured in lymphocytes from these two classes of patients. Other compounds are also being investigated to see if they have a differential effect on lymphocytes from normals and those with open-angle glaucoma.